1. Field of the Invention
The invention relates to display devices, and more particularly to structures and methods of manufacturing video displays having high luminescence.
2. Description of the Related Art
In video display technology, the traditional structure of the phosphor pattern on the display faceplate leads to loss of luminescence, or brightness. When emitted electrons, from an an electron gun in a CRT (Cathode Ray Tube) device or from field emission structures in an FED (Field Emission Display), strike phosphor elements on the faceplate, light energy in the form of photons are emitted and travel in various directions out of the phosphor.
FIG. 1 illustrates a typical FED, in which there is a backplate 10 having cathode stripes 12 and electon-emitting elements 14, mounted opposite and parallel to a faceplate 20 having phosphors 22, anode 24 and glass face 26. Electrons 28 are emitted from elements 14 in the presence of a strong electric field, and are accelerated toward the anode 24, which is raised to a voltage higher than the cathode. As electrons 28 strike the phosphors 22, light in the form of photons is emitted. Some light 30 travels directly through the glass face and may be viewed by an observer looking at the display. Other light which strikes the anode 24 and glass 26 at other than normal angles is bent due to the differing indices of refraction of the various elements. For example, the refractive index of phosphor is more than 2.5, while that of ITO (indium tin oxide), a typical anode material, is 2.0, and glass is about 1.5. This causes some light 32 to exit the glass at low angles, and other light 34 to never exit the glass. Further, some light 36 is emitted from the phosphor parallel to or away from the glass face and never exits.
It is estimated that at least 35% of the phosphorescent light is lost due to these mechanisms. This light loss generates heat inside the display. As heat builds up, phophorescence will saturate due to the thermal quench effect. As the temperature increases, the phosphorescence chroma changes and the brightness of the phosphorescence decreases.
FIG. 2 illustrates a faceplate for a CRT of the prior art. Phosphors 46 are formed between contrast-providing elements (black matrix) 42, and are covered by aluminum layer 44. Light 48 that is emitted parallel to or away from the glass face 40 is lost in internal reflection off the aluminum and does not enhance display brightness. Other disadvantages in the fabrication of this structure include the requirement of four separate lithographic steps (one for each of the three color phosphors, assuming a color CRT, and one for the black matrix), and a lack of self-alignment of the phosphors to the black matrix.